Season seafood with cajun seasoning and set aside. In large pot melt 1/2 lb of butter. To this add chopped celery, onion, bell pepper, garlic, and tobasco. Cook slowly until onions are transparent. Add chicken broth and seafood. Bring to a boil then immediately turn heat down low and cook very slowly for 20 minutes stirring often. Dissolve cornstarch in 1/2 cup of the liquid and stir until smooth. Add this to the rest of the mixture. Add green onions and parsley, and more seasoning if needed. Cook 10-15 minutes more. Serve as is or over rice.